Solar heating systems of various types are well known, but as a result of the fossil fuel crisis, such systems have recently attracted greater interest.
Usable solar energy, like usable wind energy and tide energy, is only obtainable intermittently. However, the success of any energy source can be measured by the regularity and reliability with which it can supply the needs of the user. In a building heating and cooling system, this measure of success can be translated into the capability of supplying or removing thermal energy from the living space without the use, or with a minimum use, of auxiliary and back up systems. Regularity and reliability in the intermittent solar energy source is, of course, obtained through the use of a thermal energy storage system. The success of any solar energy system, therefore, is largely dependent upon the energy storage capacity of the system.
Selection of an optimum thermal energy storage system for a building involves considerations of climate, location, insulation, size, material costs, heating and cooling requirements, etc. The most widely used thermal energy storage systems for domestic heating and cooling are water and rocks. Water has the highest heat capacity per weight, volume and dollar value of any conventional, commonly available material. Water can be easily stored and transmitted throughout the system from the solar collectors, to the storage areas and to the heat exchangers. On the other hand, thermal storage in rocks is only about 30% to 40% as efficient per unit volume as thermal storage in water because of the difference in the specific heat or rocks. Consequently, thermal storage in rocks requires a larger storage area. Rock thermal storage systems require a closed-air circulation loop between the solar collectors and the rock bins and an additional closed-loop system between the rock bins and the living space. Studies comparing system cost and thermal storage capacity show that the minimum coverage operating costs in a water system are achieved when about 10 to 15 pounds (or more) of water storage per square foot of collector area is used. In a rock storage system, 1 cubic foot of rock is required per square foot of collector area (about 3 times more volume than water).
Analysis of both water and rock thermal storage systems coupled with other system component costs, efficiencies, space-limiting factors, etc., indicate that water is the simplest and least expensive means for the collection, storage and transfer of solar energy. The chief disadvantage of a water system is the potential damage which could occur if the system should have a leak.
A typical, conventional solar heating system is comprised of a solar collector, one or more heat storage areas which, for water, consist of large tanks and, for air, usually consist of a rock filled enclosure, a heat exchanger which replaces the conventional furnace, and a piping system for distributing a primary coolant between the solar collectors, the heat storage area, and the heat exchanger.
Most of the conventional solar heating systems use a primary coolant of water or air. The components are frequently fabricated from metal and this requires special paints and coatings. To prevent freezing and scale deposits in the water systems, the conventional systems require the use of antifreeze and chemical additives. When a conventional solar heating system is combined with a conventional cooling system, the cost of this system becomes prohibitively expensive and special skills and tools are required for installation because of component complexity, and the interconnecting piping systems. Furthermore, many of the conventional systems cannot be retrofitted into existing structures because of the weight and size requirements of the solar collectors and the storage tanks.
There are many conventional solar heaters or collectors disclosed in the prior art. The following United States patents disclose typical conventional units: Masters U.S. Pat. No. 3,513,828; Hay U.S. Pat. No. 3,563,305; Hay U.S. Pat. No. 3,450,192; Andrassy U.S. Pat. No. 3,022,781; Skiff U.S. Pat. No. 1,074,219; Gough et al U.S. Pat. No. 3,076,450; Schoenfelder U.S. Pat. No. 3,951,128; Danner U.S. Pat. No. 1,473,018; Duncan U.S. Pat. No. 3,089,480; Andrassy U.S. Pat. No. 3,039,453; Abbot U.S. Pat. No. 1,801,710; Severy U.S. Pat. No. 937,013; Stout et al U.S. Pat. No. 3,918,430; and Crawford U.S. Pat. No. 3,859,980.
Briefly considering some of the most relevant of the foregoing patents, the Masters patent discloses a solar water heater utilizing a plastic bag having an upper compartment filled with air and a plurality of lower compartments through which the water flows. The Andrassy U.S. Pat. No. 3,022,781 discloses a solar water heater having a water compartment comprised of a flexible plastic top and bottom with a plurality of fluid conduits interconnecting an upper and lower header, the plastic top being transparent and the plastic bottom being black, and a wooden frame for supporting the water compartment. The Stout et al patent discloses a solar heating panel having a rectangular frame made from rigid, foam plastic material, an upper plastic cover, a water compartment comprised of a reflective bottom and a flexible top joined together so as to form a plurality of spaced apart, parallel water channels. The Skiff patent discloses a solar heater having a channel shaped upper glass lens forming a top cover of the heater for focusing the solar rays. The aforementioned Hay patents also disclose a solar heating system utilizing a plurality of flexible water storage containers located in the ceiling, floors and walls of a structure.
In general, conventional solar heating and cooling systems, and their associated conventional components, fail to provide an integrated, relatively inexpensive, easy to assemble, efficient system which can be constructed from inexpensive and lightweight components.